Iron chromium manganese alloy



Patented Aug. 2, 1949 IRON CHROMIUM MANGANESE ALLOY Henri J olivet, Albertville, France, assignor to Societe DElectro-Chimie, DElectro-Metallurgie et des Acieries Electriques DUgine, Paris,

France, a corporation of France N Drawing. Application July 4, 1945, Serial No. 603,280. In France June 9, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires June 9, 1962 2 Claims.

It is known that iron-chromium-manganese alloys containing from 6 to 40% chromium, 6 to 40% manganese, up to 1% carbon and, more particularly, from to 25% chromium, from 6 to manganese and less than 0.2% carbon, possess interesting properties as to their resistance to corrosion.

The obtention of industrial objects from technical alloys of this kind supposes the simultaneous presence of a certain number of characteristic features which are substantially the following ones:

(at) These alloys must be capable of being deformed at a high temperature, for instance by forg ng, rolling Or other similar operations under industrially satisfactory conditions.

(b) These alloys must also be able to be shaped at ordinary temperature, for instance thru stretching, swaging or other deforming actions or to be assembled by welding, all this under conditions which must also be industrially satisfactory.

(c) These alloys must possess a mechanical strength and an absence of fragility leading to high characteristic features of elongation on drawing and of resilience under shocks.

(d) Finally, these alloys must be able to be submitted, either in the course of their cooling or in the course of preheating, such as, for instance, in operations of heat treatment or in welding operations, to a sojourn in a zone of temperature of 500 to 800 C. without acquiring a particular sensibility to the phenomenon known as intercrystalline corrosion.

If this condition is not fulfilled the attack of of 18-8 chromium-nickel alloys, technical alloys are obtained which are capable of giving satisfaction in the realization of industrial objects answering the above indicated satisfactory conditions.

On the contrary, studies concerning stainless ferrous chromium-manganese alloys have shown that though the lowering of the carbon content has a favourable action, this measure is absolutely insufficient, when used alone, for avoiding intercrystalline corrosion.

corrosives such as, for instance, acids or aggressive saline solutions during or after this sojourn leads to a loss of the metallic brightness, of the sonority, of the mechanical strength and of the ductility.

In the case of stainless chromium-nickel alloys and more particularly those of the 18-8 type (18% chromium and 8% nickel) it has been proposed, in order to avoid the production of this corrosion phenomenon, either to cause these alloys to have a very small carbon content, or to add to these alloys one or more elements of addition such as tungsten, molybdenum, niobium, vanadium and especially titanium in quantities varying according to the carbon content of the alloy, the best results being obtained when the alloy element is, in this latter case, in a proportion at least equal to four times the carbon content.

Experience has shown that by following one or the other of these prescriptions in the case As a matter of fact, chromium-manganese alloys having a carbon content of even less than 0.03%, which is the lowest which it is actually possible to realize technically, are still exposed to that corrosion in an important manner.

Thus, for instance, a stainless chromium-nickel alloy with 18% chromium and 10% nickel having a carbon content of 0.1%, quenched at 1,100 C. and annealed at the maximum sensibilization temperature (650 C.) has given, after a treatment of 72 hours with boiling Monypenny reagent, a loss of weight of 5 to 7 milligrams per square centimetre, has lost its sonority and cracked on folding to while a similar alloy titrating only 0.3% carbon has shown, when submitted to the same treatment conditions, a loss of weight of 0.5 to 1 milligram per square centimetre, has given no loss of sonority and no crack on folding. On the other hand, a chromiummanganese alloy containing 18% chromium and 10% manganese, having a carbon content of 0.1 quenched at 1,100 C. and annealed at the maximum sensibilization temperature (600 C.) has shown, after a treatment of 72 hours with boiling Monypenny reagent, a loss of weight of milligrams per square centimetre, has lost its sonority and cracked on folding to 90, while a similar alloy titrating only 0.3 of carbon treated under the same conditions still showed a loss of weight of 20 to 35 milligrams per square centimetre, had lost its sonority and cracked on folding at 90.

As may be seen, this constitutes an essential difference of behaviour between both groups of alloys.

It has been proposed of doing away with the intercrystalline corrosion phenomenon by adding to the chromium-manganese alloys elements such as, for instance, titanium, which are known for their favourable action in the case of the chromium-nickel alloys and this in the same proportions of at least four times the carbon content.

Experience shows in this case that, subject to 3 the incorporation, with the said alloys, of a higher proportion of addition elements than that which is necessary in the chromium-alloys of the 18-8 type, it is still possible to obtain the desired result as regards the fact of doing away with the intercrystalline corrosion. But the application of these prescriptions is by no way sufficient for obtainin technical alloys answering the above indicated conditions.

Thus, for instance, a chromium-nickel alloy titrating 18% chromium, 10% nickel, 0.04% carbon and 0.2% titanium has shown, when tested under the above mentioned conditions of .treatment, a loss of weight of 0.5 to 1 milligram per square centimetre, no loss of sonority and has been able to be folded home without cracking. This alloy was capable of being easily rolled and possessed after quenching at 1,l C. a strength of 60 kilograms per square millimetre, an elongation of 50% and a Mesnager resilience of 3'7 kilogrammetres, while, on the other hand, a chromium-manganese alloy titrating 18% chromium, 11% manganese, 0.04% carbon and 0.2% titanium has shown, when tested under the above specified conditions of treatment, a loss of weight of 15 to 17 milligrams per square centimetre and has cracked on folding to 90.

If, inspiring oneself from known facts, one increases the proportion of the additions, the intercrystalline corrosion is done away with, but the alloy shows a high fragility and is no longer capable of being shaped thru swaging nor of being welded. For instance, a chromium manganese alloy titrating 18% chromium, 11% manganese, 0.05% carbon and 0.35% titanium has shown, when tested under the above mentioned conditions of treatment, a loss of weight of 0.5 to 1 milligram per square centimetre and has been folded without cracking. However, this alloy, which could easily be rolled, possessed, after quenching at 1,100 C. a strength of 55 kilograms per square millimetre, an elongation of 2% and a Mesnager resilience of 0.5 to 1 kilogrammetre and could be neither swaged nor welded.

Therefore, if the specialist simply attempts forthwith to manufacture industrial apparatus by using chromium-manganese alloys according to the indications of literature, experience shows that he will not be capable of obtaining the desired result such as above defined in paragraphs (a) to (d).

On the other hand, it has been proposed to substitute manganese by nickel in chromium-manganese alloys in a proportion going up to half the manganese content without this having any prejudicial action and, on the contrary, with this result that certain features as to the mechanical strength are increased.

When this substitution is effected in the proposed limits in chromium-manganese alloys containing titanium, this new fact has appeared that the so-obtained alloy was no longer capable of being shaped by rolling in a heated state or forging under industrially satisfactory conditions, though it answered the particulars given in the literature.

v Thus, for instance, a chromiummanganese alloy containing 18% chromium, 9% manganese and 2.5% nickel, 0.05% carbon and 0.2% titanium, i. e. an alloy comparable to the above specified alloy with 12% manganese, has cracked in a very important manner in the course of rolling in a heated state while it possessed after quenching a strength of 70 kilograms per square millimetre, an elongation of 30% and a Mesnager resilience of 4 25 kilogrammetres. This disadvantage is essentially connected with the addition of nickel, as shown by the experience obtained, in this respect, thru the study of chromium-manganese containing no titanium. Thus, for instance, a chromiummanganese alloy containing 18% chromium, 9% manganese, 2.5% nickel and 0.05% carbon has not been capable of being rolled in a heated state nor forged under the usual conditions though it possessed after quenching a strength of '75 kilograms per square millimetre, an elongation of 45% and a Mesnager resilience of 35 kilogrammetres. This proves that the addition of nickel in the above specified limits, which addition effectively possesses a favourable and previsible action on the mechanical properties, exerts an unfavourable action, which cannot be foreseen, on work facility at high temperature. This further explains, more particularly, the reason why the chromium-manganese alloys-while their properties as to corrosion in certain mediums are equivalent and their cost lowerhave not been substituted hitherto for the chromium-nickel alloys, for the manufacture of apparatus adapted for the chemical industry.

In spite of the conclusions which could be drawn from the preceding statement, viz. that no satisfactory solution of the problem as put above appears to be possible in the domain of ferrous chromium-manganese alloys, it has been found, thru the present invention, that it is possible to realize industrial alloys in which the unfavourable influence of titanium on the mechanical features and of an addition of nickel on the possibilities of working in a heated state mutually correct themselves on the actual condition that certain definite proportions between the carbon, titanium and nickel contents are realized, viz., in alloys containing from 15 to 19% chromium, '7 to 15% manganese and up to 0.1% carbon, a proportion Ti/C which is higher than 6 and a proportion Ni/Ti between 3 and 8. One has specified above the case of alloys in which the first condition (proportion Ti/C' higher than 6) was not realized and which have not withstood the intergranular corrosion, and the case of alloys for which the nickelcontent was too high with respect to the titanium content, that is to say exceeded the ratio 8.

The following example can furthermore be given: A chromium-manganese alloy containing 18% chromium, 9% manganese, 0.05% carbon, 0.35% titanium and only 0.6% nickel has been capable of being rolled or forged without any difficulty. When tested under the above specified conditions of treatment, it has shown a loss of weight of 0.5 to .1 milligram per square centimetre and has been folded home without crack, but after quenching at 1,100 C. it had a strength of 60 kilograms per squared millimetre with an elongation of 2% and a Mesnager resilience of 0.7 kilogrammetre; it has not been capable of being swaged nor welded.

Therefore, in the limits indicated for the composition of chromium-manganese alloys, it is within the thus defined domain and this domain alone that it is possible to meet simultaneously the above enumerated conditions which are indispensable for the realization of industrial apparatus liable to corrosion, especially to the intercrystalline corrosion which can occur after heating in the zone of temperatures comprised between 500 and 750 C.

Thus, according to the invention, a. stainless chromium-manganese alloy containing 18% chromium, 10% manganese, 2% nickel, 0.05% carbon and 0.35% titanium has been capable of being rolled in a heated state without difiiculty. When tested under the above specified conditions of treatment it has shown a loss of weight of 0.5 to 1 milligram per square centimetre, no fragility on folding and after quenching at 1,100 C., a strength of 65 kilograms per square millimetre, an elongation of 35% and a Mesnager resilience of 35 kilogrammetres.

The other compositions of alloys in which the proportions were comprised between the above specified limits for chromium, manganese, nickel, carbon and titanium and in which the proportions of titanium to carbon and of nickel to titanium were higher than 6 and between 3 and 8 respectively have been found capable of being rolled in a heated state, stretched and swaged in the cold, welded, have shown little fragility and have withstood surface corrosion and intercrystalline corrosion though having been brought to a temperature comprised between 500 and 800 C. and though they had not been quenched after having been submitted to said temperature.

What I claim is:

1. An alloy comprising about 18% chromium,

6 about 10% manganese, about 0.05% carbon, about 0.35% titanium, about 2% nickel, and the remainder iron.

2. An alloy comprising about 15% to 19% chromium, about 7 to 15% manganese, about 0.05% carbon, about 0.35% titanium, about 2% nickel, and the remainder iron.

HENRI J OLIVET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,138,289 Becket et a1 Nov. 29, 1938 2,153,906 Aborn et a1. Apr. 11, 1939 2,198,598 Becket et a1 Apr. 30, 1940 2,358,799 Franks Sept. 26, 1944 OTHER REFERENCES Alloys of Iron and Chromium, High Chromium, pages 468, 469, 470. Edited by Kinzel and Franks. Published in 1940 by McGraw-Hill Book Co., New York. 

